Using the addon is very straightforward. Simply make sure a camera is the active object, right–click it, and choose Link to Monitor. You'll then be prompted to pick a base material for your display. Once confirmed, a plane with the monitor material will appear at the 3D cursor location.

You can use this plane as it is, or apply the new material to any other object. Just make sure the object's UV map covers the full UV area vertically so the display looks correct.

From that point on, any changes you make to the camera — such as location, rotation, focal length, or sensor size — will automatically update in the monitor material.